Text for questions number 67-69.

    The variety of fish reproduction techniques provides an example of the adaptive complexity that ecologists have found. Most spawning is synchronized with phases of the moon, and eggs are fertilized in the water column. However, some species lay eggs on the sea bottom or in a protected area. Damselfishes will guard their nests quite aggresively while jawfish and cardinalfish incubate eggs in the mouth. Seahorse and pipefish carry their eggs in a pouch.

    Most hermaphroditic species follow the protogynous pattern of the fairy basselet. If the male disappears, the dominant female in his harem will change sex within days and take over his role within hours. However, a few species are protandrous, where the fish are male first and then become female. Much remains to be learned about fish reproduction, and evolutionary biologists find that the coral environment provides them with many opportunities to observe a variety of species and specialized behaviours.

    The reef itself is alive with many billions of coral colonies plus other limestone-depositing organisms, growing among the skeletons of their predecessors. Reefs grow on the continental shelf edge, on the shelf itself, along islands and atolls, and from the continental mainland. While strict requirements concerning the amount of available light, and the ocean's clarity, temperature, and movement have restricted the geographic locations of the Earth's reefs, these requirements have not limited the ecological complexity of reef communities.

    Species representing more phyla than those found in a tropical rainforest live on coral reefs. Scientists counted 1,441 worms on one coral head alone, and these worms belonged to over a hundred different families. Six of the Earth's seven species of marine turtles inhabit the Great Barrier Reef. Four thousand species of fishes, more than a third of all marine fish species, make coral ecosystems their home. Perhaps more notably, representatives from all fish families and most genera are reef inhabitants.

    Scientists study reef fishes not only because of the diverse sampling of species but also because of the range of behaviours and relationships between species and other animals that is available for analysis. Intense competition and predation have caused fishes to carve out special niches. Mimicry and camouflage offer just two ways for species to blend in with their surroundings. Symbiotic relationships between fish and other organisms also occur with frequency on coral reefs. The anemonefish share their habitat with sea anemones in a symbiotic relationship that scientists have yet to unravel completely. The defensive nematocysts of the anemone are used to stun prey, but the anemonefish are resistant to these stinging cells. Researchers believe that the fish secrets a mucous coating that mimics that of the anemone allowing for chemical signals to prohibit the firing of the cells. One theory holds that the fish obtain these chemicals by rubbing against the sea anemone's tentacles. The benefits, if any, to the anemone for having these fish live with them is not clear.

The author discusses the number of species found on a coral head in the fourth paragraph in order to ....